1. Field of the Invention
This invention relates to a process for preparing a nonwoven fabric of thermoplastic, synthetic organic fibers. More particularly, the invention concerns such a process and a novel product produced thereby. The process involves the steps of needling, heating, burnishing and cooling.
2. Description of the Prior Art
Processes are known for making strong, permeable nonwoven fabrics having at least one abrasion-resistant surface. For example, Platt et al., U.S. Pat. No. 4,042,655 and Erikson, U.S. Pat. No. 4,342,813 disclose processes wherein batts of polypropylene fibers are subjected in sequence to needling, infra-red heating, calendering, cooling and winding up. Such fabrics have been suggested for use in lamination, furniture tickings, mattress-spring pocketting and the like. In several of these end uses, the nonwoven fabric requires special characteristics, in addition to the usually desired high strength and tear properties. For example, to function well as a mattress-spring pocketting, the nonwoven fabric should have at least one highly abrasion-resistant surface and sufficient permeability to permit the quiet passage of air in and out of the pocketting during repeated in-use compressions and expansions of the mattress springs. As another example, to function well in certain lamination uses (e.g., wallpaper), the nonwoven fabric should have one abrasion-resistant surface and an opposite surface that accepts adhesives well.
Although not concerned with the above-described types of products or processes, Thiebault. U.S. Pat. No. 4,363,682 discloses a method for making an electric filter face mask in which a fluffy surface layer of a nonwoven, highly aerated mass of polypropylene fibers is smoothed by being heated under low pressure and light friction by a metal mass having a temperature between 115.degree. to 150.degree. C. to form a skin or porous glaze on the surface.
Each of the above-described processes provides a nonwoven fabric which has at least one relatively abrasion-resistant surface whose characteristics differ considerably from those of the mass of fibers beneath the surface. However, the utility of these products could be enhanced significantly by improvements in the uniformity of the surface and/or the strength of the fabric. A purpose of this invention is to provide a process for making such improved fabrics.